From 5b3e29f8092570a457d7b817db5e3bed95f72341 Mon Sep 17 00:00:00 2001
From: Michael Li <michaelli65535@gmail.com>
Date: Wed, 9 Jul 2025 02:22:33 +1000
Subject: [PATCH] text splitters: add chunk_size and chunk_overlap validations
 (#31916)

Thank you for contributing to LangChain!

- [x] **PR title**: "package: description"
- Where "package" is whichever of langchain, core, etc. is being
modified. Use "docs: ..." for purely docs changes, "infra: ..." for CI
changes.
  - Example: "core: add foobar LLM"


- [x] **PR message**: ***Delete this entire checklist*** and replace
with
    - **Description:** a description of the change
    - **Issue:** the issue # it fixes, if applicable
    - **Dependencies:** any dependencies required for this change
- **Twitter handle:** if your PR gets announced, and you'd like a
mention, we'll gladly shout you out!


- [x] **Add tests and docs**: If you're adding a new integration, please
include
1. a test for the integration, preferably unit tests that do not rely on
network access,
2. an example notebook showing its use. It lives in
`docs/docs/integrations` directory.


- [x] **Lint and test**: Run `make format`, `make lint` and `make test`
from the root of the package(s) you've modified. See contribution
guidelines for more: https://python.langchain.com/docs/contributing/

Additional guidelines:
- Make sure optional dependencies are imported within a function.
- Please do not add dependencies to pyproject.toml files (even optional
ones) unless they are required for unit tests.
- Most PRs should not touch more than one package.
- Changes should be backwards compatible.

If no one reviews your PR within a few days, please @-mention one of
baskaryan, eyurtsev, ccurme, vbarda, hwchase17.
---
 libs/text-splitters/langchain_text_splitters/base.py        | 6 ++++++
 libs/text-splitters/tests/unit_tests/test_text_splitters.py | 5 +++++
 2 files changed, 11 insertions(+)

diff --git a/libs/text-splitters/langchain_text_splitters/base.py b/libs/text-splitters/langchain_text_splitters/base.py
index f9e4a92222a..8861f4c6585 100644
--- a/libs/text-splitters/langchain_text_splitters/base.py
+++ b/libs/text-splitters/langchain_text_splitters/base.py
@@ -47,6 +47,12 @@ class TextSplitter(BaseDocumentTransformer, ABC):
             strip_whitespace: If `True`, strips whitespace from the start and end of
                               every document
         """
+        if chunk_size <= 0:
+            msg = f"chunk_size must be > 0, got {chunk_size}"
+            raise ValueError(msg)
+        if chunk_overlap < 0:
+            msg = f"chunk_overlap must be >= 0, got {chunk_overlap}"
+            raise ValueError(msg)
         if chunk_overlap > chunk_size:
             msg = (
                 f"Got a larger chunk overlap ({chunk_overlap}) than chunk size "
diff --git a/libs/text-splitters/tests/unit_tests/test_text_splitters.py b/libs/text-splitters/tests/unit_tests/test_text_splitters.py
index 6f03a2d59f0..1d3304d1b84 100644
--- a/libs/text-splitters/tests/unit_tests/test_text_splitters.py
+++ b/libs/text-splitters/tests/unit_tests/test_text_splitters.py
@@ -212,6 +212,11 @@ def test_character_text_splitting_args() -> None:
     """Test invalid arguments."""
     with pytest.raises(ValueError):
         CharacterTextSplitter(chunk_size=2, chunk_overlap=4)
+    for invalid_size in (0, -1):
+        with pytest.raises(ValueError):
+            CharacterTextSplitter(chunk_size=invalid_size)
+    with pytest.raises(ValueError):
+        CharacterTextSplitter(chunk_size=2, chunk_overlap=-1)
 
 
 def test_merge_splits() -> None: